The present subject matter relates generally to the field of semiconductors and, more particularly, to dual-member pellicle assemblies and methods of use.
In semiconductor processing, a photolithographic mask (photomask) is used to pattern a radiation sensitive layer on a semiconductor substrate. Typically, the radiation sensitive layer is called a photoresist layer. A xe2x80x9cphotomaskxe2x80x9d is defined herein as the combination of a photomask substrate and a patterning material. Typically, the substrate comprises a quartz or glass plate, which is transparent to the exposing radiation, and the patterning material lies on one side of the substrate and typically comprises chrome, aluminum, or gold, which is opaque to the exposing radiation. A stepping field is the portion of the patterning material that is used to pattern the photoresist layer.
The photoresist layer is sensitive to photomask defects, such as particles, for example. If a particle is present on a photomask within the stepping field when a photoresist layer is exposed using the photomask, the particle may cause a corresponding image to be formed in the patterned photoresist layer, which in turn may cause the device being fabricated to fail. If the stepping field of the photomask contains only one die, then all die on the semiconductor substrate may fail.
A pellicle is typically used to reduce the likelihood that particles migrate onto the stepping field of a photomask. A xe2x80x9cpelliclexe2x80x9d is defined herein to include a pellicle frame and a pellicle membrane or sheet. The pellicle sheet is typically a flat, usually organic material, such as nitrocellulose or cellulose acetate, and it may be coated with one or more layers of fluoropolymers.
FIG. 1 illustrates a perspective view of prior art semiconductor photolithography equipment 1, including a prior art pellicle. The equipment 1 includes an illumination optical system 2, including a source 4 of photolithographic radiation 6. The equipment 1 further includes a photomask substrate 10 having on its surface 12 a photolithographic pattern 14. The photomask comprises substrate 10 and photolithographic pattern 14.
To protect the photomask, a pellicle comprising pellicle frame 16 and pellicle membrane 20 is positioned a certain distance over the photomask. Pellicle frame 16 is typically a single-walled frame of metal, metal alloy, or plastic. Pellicle membrane 20 is typically securely fastened to pellicle frame 16 via an adhesive or adhesive tape (not shown).
A pellicle may be secured to a photomask to protect it from particles within the photolithography area. Photolithography is done in an ambient environment where particles are usually present, even in the cleanest of clean-room environments. Cleaning particles from the photomask can be difficult because of the relatively tight spacing between the photomask and the pellicle membrane. To properly clean a photomask and its pellicle often requires that they be removed from the photolithography area to the mask shop for several hours or even days, at a significant expenditure of production resources, and the production of semiconductors can possibly be delayed.
The line dimensions of semiconductor devices are constantly shrinking. In order to achieve smaller patterning dimensions, photolithography must be carried out at increasingly shorter wavelengths. However, organic pellicle membranes typically cannot be used for shorter wavelengths. The high energy of the photons absorbed by the pellicle membrane can cause a chemical reaction in or near the pellicle membrane, causing it to deteriorate. Further, at wavelengths of approximately 200 nanometers (nm) and below a reaction occurs between the radiation and the air between the photomask and the pellicle membrane, producing ozone, which can break down organic pellicle membranes. In some instances, the pellicle membrane becomes physically damaged during only one exposure to the radiation.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a significant need in the art for a pellicle device that can readily be removed and reattached without costly or complicated procedures such as cleaning, adhesive application, and so forth, as well as for methods of operating such a pellicle device.